Discovery is the process whereby neighboring nodes on either side of a link automatically determine each others' identity and verify the connectivity between them. There can be “layer adjacency discovery” between nodes that have interfaces or switching capabilities at the same layer, and “physical adjacency discovery” between nodes that have interfaces or switching capabilities at different layers. Current International Telecommunications Union—Telecommunications Division (ITU-T) standards and Optical Internetworking Forum (OIF) implementation agreements define methods for layer adjacency discovery, wherein there is a bidirectional link available between neighboring nodes, using the control overhead bytes present in Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) and Optical Transport Network (OTN) formatted links (see, for example, ITU-T Recommendations G.7714 and G.7714.1, and OIF User Network Interface (UNI) 1.0 Signaling Specification). Likewise, the Internet Engineering Task Force (IETF) defines a “link management protocol” that does not perform automatic discovery, as the Internet Protocol (IP) addresses of neighboring nodes must first be configured into the system, but that can be used after discovery, or with configured information, to exchange link capabilities and verify connectivity (see Internet Draft).
Thus, layer adjacency discovery is logically performed at a specific layer (i.e., discovery can be at the fiber wavelength or SONET path/line/section (OTN ODU/OTU) layers). While the provisioning of such information is not difficult, the provisioning process is typically a manual process with several steps that may lead to errors being incorporated into a topology database. Any method that increases the accuracy of the topology database is helpful to carriers, and an automated or partially-automated method is most useful.
ITU-T and OIF layer adjacency discovery methods rely on the existence of a bidirectional link between neighboring nodes at a specific layer and the availability of an in-band channel at that specific layer over which a discovery message can be sent, unimpeded by any equipment placed in between the neighboring nodes that operates at a different layer. SONET/SDH and OTN control overhead bytes are designed to be passed transparently by equipment at a lower layer (e.g., path overhead is passed transparently by line and section terminating equipment, line overhead is passed transparently by section terminating equipment, etc.). Certain fields, such as bit error monitoring bytes (BIP-8), are created based on the bit values in a frame, and if any information in the control overhead bytes is changed by intervening equipment, this either invalidates the bit error monitoring bytes (potentially causing an error indication) or requires that the intervening equipment modify the bit error monitoring bytes to correct for the change in the control overhead bytes.
If either a bidirectional link is not available or a peer relationship does not exist, standard discovery methods do not work. If neighboring nodes are not peers (i.e., do not operate at the same layer), then one endpoint may be able to write information into the control overhead bytes, but the other endpoint may not, as its role is normally to pass the control overhead bytes transparently. In particular, if a node which normally passes the control overhead bytes transparently is called upon to write information into the control overhead bytes, this disrupts the parity bits used for performance monitoring on the frame and an intervening node may have to recalculate the parity bits. This may also result in a false performance monitoring reading at the node terminating the frame. If only a unidirectional link is available, only one node will receive its neighbor's identity.
This makes it complex and costly for equipment to use standard discovery methods if the equipment is not operating at a peer layer, since equipment operating at a lower layer cannot modify overhead by inserting its own address and information without correspondingly recalculating the bit error monitoring bytes. Moreover, equipment operating at a lower layer cannot be designed to insert information into overhead, since this is not a standard function. Monitoring the contents of overhead, however, is a useful function and can be used to determine, for example, the performance of a transported signal.
Thus, what is needed in the art is an automated discovery method for equipment that does not operate at a peer layer and, as a result, cannot perform bidirectional interaction using control overhead bytes to detect the address/identity of a physically adjacent node. What is also needed in the art is a method for using out-of-band protocol messages, such as Link Management Protocol (LMP) messages (or other protocol messages as defined in the ITU-T standards for link capability exchange), to allow equipment to carry its own address/node identification (ID) and link information back to the physically adjacent node. A method for the authentication of the received out-of-band message is desirable in order to ensure that the received out-of-band message was generated by an actual neighboring node, since out-of-band messages can presumably be received from any node connected to the same control network.